The present invention is directed to an ion source, particular to an ion source using a cathodic vacuum arc, and more particularly to an ion source using a filtered cathodic arc for the production of dense, adherent coatings, wherein the filtering eliminates or reduces macro-particles normally produced by the cathodic arc.
Coatings produced by traditional physical vapor deposition (PVD) techniques, such as electron-beam evaporation and magnetron sputtering are adequate for many purposes. However, these are increasingly frequent instances where coatings produced by a PVD technique have inadequate stoichiometry, adhesion, or density.
Ion-based coating methods have the potential to produce superior coatings due to the ability to control the arrival energy of the ions. Ion sources involving vacuum arc-based processes offer the prospect for overcoming the difficulties relative to the PVD techniques by making use of their ability to provide copious quantities of ions of virtually any conductive material. Vacuum arc coating techniques generally involve use of either an anodic arc or a cathodic arc, with the cathode arc technique being of either a pulsed or continuous type.
Cathodic vacuum arc systems for coating applications are relatively new, although it has been recognized for decades that coatings could be produced using a vacuum arc. The historical background and development of vacuum arcs is set forth in an article entitled "Review of Ion-Based Coating Processes Derived from the Cathodic Arc" by David M. Sanders, J. Vac. Sci. Technol., A7 (3), May/June 1989, pp. 2339-2345, and in an article entitled "Coating Technology Based on the Vacuum Arc-A Review" by D. M. Sanders et al., IEEE Trans. Plasma Sci. 18 (6), pp. 883-894, 1990.
While it has been recognized for some time that cathodic arcs can provide a copious source of ions for the production of coatings in a vacuum system, it has also been recognized that such arcs normally produce droplets of material called macro-particles which lead to blemishes in the coatings thus produced. The separation or elimination of macro-particles from the ion flux produced by a cathodic arc discharge has long been the goal of many research efforts. A number of approaches have been advanced for the removal of such macro-particles, which include the use of filtering and such are exemplified in the above-referenced articles. Also, see an article entitled "Transport of Plasma Streams in a Curvilinear Plasma-Optics System", Sov. J. Plasma Phys., 4 (4), pp. 425-428 July-August, 1978, I. I. Aksenov et al. However, these prior approaches have not resulted in providing both an effective ion source and a means for eliminating or reducing the macro-particles produced by the cathodic arc techniques.
Therefore, there has existed a need for an ion source based on the cathodic arc discharge which is capable of producing coatings without blemishes caused by macro-particles. The present invention fulfills the prior need by providing an ion source using the cathodic vacuum arc for producing large currents of positive ions of a wide variety of materials, wherein the ions produce coatings with improved properties such as high density and adhesion, while the coatings are essentially free of blemishes caused by macro-particles, the macro-particles having been filtered out.